Agile development aims at switching the focus from processes to interactions between stakeholders, from heavy to minimalistic documentation, from contract negotiation and detailed plans to customer collaboration and prompt reaction to changes. With these premises, requirements traceability may appear to be an overly exigent activity, with little or no return-of-investment. However, since testing remains crucial even when going agile, the developers need to identify at a glance what to test and how to test it. That is why, even though requirements traceability has historically faced a firm resistance from the agile community, it can provide several benefits when promoting precise alignment of requirements with testing. This paper reports on our experience in promoting traceability of requirements and testing in the data communications for mission-critical systems in an industrial Scrum project. We define a semi-automated requirements tracing mechanism which coordinates four traceability techniques. We evaluate the solution by applying it to an industrial project aiming at enhancing the existing Virtual Router Redundancy Protocol by adding Simple Network Management Protocol support.